Flames can be seen from the air after an explosion happened at the sight of a train derailment in southern Jefferson County, just south of Louisville, Ky, Wednesday, Oct. 31, 2012. (AP Photo/The Courier-Journal, Sam Upshaw)

Billy Ash, Mayor of West Point updates residents of West Point, Ky., living within a mile-and-a-half radius of the site of a train derailment as they wait at a Red Cross shelter Wednesday, Oct. 31, 2012 at the Muldraugh Elementary School in Muldraugh, Ky. A Paducah & Louisville Railway train carrying hazardous chemicals derailed just after 6 a.m. EDT Monday, A leak of a potentially explosive material was contained, but authorities say three workers were severely burned in a fire that erupted while contractors were removing debris from the train today in southwest Louisville, Kentucky. (AP Photo/Brian Bohannon)

LOUISVILLE, Ky. (AP) — A chemical fire at the site of a train derailment in Kentucky that forced hundreds of people to evacuate their homes is expected to continue burning all day Thursday, far longer than initially predicted.

Emergency officials said they were given inaccurate information about how much of the flammable chemical, butadiene, remained in an overturned tanker car. Authorities initially estimated the fire would burn itself out within two hours, but now are reassessing how much of the chemical is left, said Doug Hamilton with Metro Louisville Emergency Management.

It wasn’t immediately clear exactly how long the fire would continue burning. Flames that reached 6 feet had been shooting out of the car and spewing thick, black smoke for almost 24 hours.

The blaze has forced the evacuation of the entire central Kentucky town of West Point, as well as people from nearby Louisville.

The evacuation order came after a cutting torch ignited vapors Wednesday while workers tried to separate two of the 13 cars that derailed early Monday. The vapors were from butadiene, a colorless, flammable gas that is a common ingredient in synthetic rubber used for tires on cars and trucks.

Three workers were taken to the University of Louisville hospital with severe burns. Authorities have not released the names of the injured workers but said one was in critical condition, while the other two were in fair condition. One was expected to be released from the hospital Thursday.

The train derailed on a line that runs between Paducah in western Kentucky and Louisville, which is home to rubber manufacturers and other chemical plants, most of them concentrated in the Rubbertown neighborhood. It was not immediately clear to which of those companies the chemicals may have been bound.

Hundreds of thousands of gallons of water were being sprayed onto the burning car and two derailed cars within a few feet in an attempt to keep the cars cool, officials said. Those cars contain hydrogen fluoride, a colorless gas with a sharp, pungent, irritating odor, according to the U.S. Environmental Protection Agency. Inhalation can cause severe respiratory damage. It is used in the glass etching, electronic and chemical industries.

"This is as bad as it gets as far as a haz-mat incident, if it were to be released," said Art Smith, an emergency coordinator with the EPA. "And we’re all very concerned about that."

Smith also said the EPA is monitoring water in the nearby Salt River because a rush of possibly contaminated water is flowing into it from the scene. Officials hurriedly erected a dam Thursday to try to contain the water.

The scene is at the confluence of the Salt and Ohio rivers.

Officials did not speculate Thursday on how the fire started.

"The workers that are here are highly trained and this is one of those freak accidents that occurs unfortunately," Lt. Col. Rick Harrison, assistant chief with the suburban Buechel Fire Department said.

Metro Louisville Emergency Management spokeswoman Jodie Duncan said the evacuation order would stay in place until the blaze was extinguished. Butadiene, which is shipped in a liquefied and compressed state, can cause irritation to the eyes, nose and throat. It can also damage the central nervous system and the reproductive system.

The Paducah & Louisville Railway train derailed Monday morning near Dixie Highway, a main corridor between Louisville and Fort Knox. Nine of the 13 derailed cars were carrying hazardous chemicals.

Residents within a 1.2-mile radius of the wreck were evacuated Wednesday and those living within a 5-mile radius were ordered to stay indoors. Also, three local schools within the areas of the evacuation or shelter-in-place orders were closed Thursday.

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